Waxy materials present in crude oils and in the high boiling fractions are considered to be crystalline throughout but under certain conditions may behave like a colloid. Certain wax solutions of refined products such as petrolatum, when agitated or mixed for long periods near or at the crystallizing temperature, will form a completely transparent jelly. But the same solution, when chilled rapidly with moderate agitation will precipitate a wax that can be centrifuged.
It was observed many years ago in the sweating of solid paraffins at the petroleum refinery that three crystalline forms (manifestations) of hydrocarbons are involved. These are known as "plate", "malcrystal", and "needle"[note, for example, The Chemistry and Technology of Waxes bu Albin H. Warth, published by Reinhold Publishing Corp. (New York, 1947) p. 239]. It was recognized that the relative proportion of these types of crystals not only has a relationship to the source of the crude but also to the process of handling the wax.
The members of each series crystallize similarly as either plates, malcrystals, or needles. If one type is present (plate, mal, or needle), the crystal form remains the same regardless of such factors as the amount and kind of solvent.
When crude oil is pumped from the ground and transported through pipelines, transported by ocean tankers, or stored in storage tanks on land or offshore, a large amount of heavy material separates and comes out of solution. The main component of this residue is high molecular weight paraffin waxes. In some cases the wax represents as much as 90 percent of the deposited residues.
The amounts of wax present in crude oil are to a large extent an indicator of its origin, whether the crude originated in Venezuela, Mexico, or Malaysia.
This mixture of wax, oil, sand, and water is referred to as "slop oil", or "slop", in the petroleum industry. The percentage of slop oil varies according to the type of crude and the conditions under which it has been transported. Usually the amount of slop oil ranges from a low of 0.5% to a high of 10%; normally, it is in the range of 2% to 5%.
For the last century and until today the only way to keep slop oil from separating from crude oil is to heat the slop oil while it is being transferred into mixing tanks with crude oil. The cost of keeping slop oil mixed with crude oil is a function of many variables such as temperature, solvent diluents, and residence time of the crude in a tank or pipeline.
The petroleum industry is plagued with the problem of having to deliver crude oil to refineries in a timely and economic manner. If a pipeline becomes plugged up or clogged because of paraffin wax precipitating out during the pumping operation, a crisis can arise. Numerous pipelines worldwide are clogged daily or monthly due to wax precipitating out of the crude oil. Daily, 50,000,000 barrels of crude oil are pumped from the ground worldwide (as of May, 1999). If 5% of the heavy residues come out of the crude oil being transported, whether by pipeline or tanker, the amount of slop oil or crude residue is 2,500,000 barrels per day. This amounts to 912,000,000 barrels per year. If 70% of this slop oil is useable crude which can be processed to refine production, then the amount of recoverable hydrocarbon equals over 640,000,000 barrels per year. At a cost of $10.00/barrel of crude oil this amounts to the recovery of $6.4 billion per year of useable hydrocarbon as either energy or petrochemical feedstock.
Another important factor in the transportation of crude oil is the corrosion of pipelines, storage tanks, and marine tankers. One of the main sites of corrosion in pipelines and storage tanks is at the point of buildup of the paraffin wax. At this site corrosion-causing chemicals become embedded in the wax and migrate to the metal surfaces. Pipelines with intrinsically large wax buildup or settling have many more corrosion problems than pipelines where the oil moves swiftly without deposition occurring. This results in increased maintenance cost and in some cases pipelines have to be shut down and crude must be rerouted to new lines as a result of both the clogged lines and corrosion. One of the main maintenance tools used to unclog crude oil pipelines is pigging the line. In this process a small device shaped like a pig with a series of scrapers on its sides is shot through the line to remove all the wax. This wax is then collected at traps located along the line and shipped to pipeline pumping stations for storage.
In storage tanks the problems associated with wax settling out are tremendous and present an extremely challenging task to refiners and terminal operators.
When crude oil remains idle and cold in a storage tank, a heavy residue forms that, over time, accumulates at the bottom of the tank and reduces useable tank volume. This residue, known as slop oil (or, slop), consists of heavy paraffinic waxes and asphaltenes which solidify in crystalline form. Slop oil is extremely difficult to remove from tanks and presents a very costly disposal problem for the refinery and terminal operator.
Traditional tank cleaning methods use a combination of heat (e.g., 60 to 75 degrees C. or greater) and mechanical agitation to force the slop oil back into solution with crude oil, so the mixture can be pumped out of the tank. In order to keep the waxes and asphaltenes in solution with the crude oil, the mixture must be kept at, for example, 75 degrees C. or greater and, in most cases, continuously circulated. The tremendous amounts of energy required to heat and circulate large volumes of dense crude oil to these elevated temperatures over long periods of time increase handling costs dramatically.
After pumping out the slop oil containing paraffin waxes and asphaltenes, the slop oil mixture must be kept hot or the wax will separate from solution, and the problems associated with slop oil will recur.
This need to use heat results in great energy cost and losses.
The preferred, exemplary chemical compound mixture described herein will perform, inter alia, the following functions:
1. Converts the wax in, for example, the slop oil from a crystalline to an amorphous material; PA1 2. Disperses the amorphous material into a diluent solvent; PA1 3. Acts as a demulsifier which separates any water present in the slop oil; PA1 4. Acts as a degreaser and works at a very low activity, e.g., 0.025%; and PA1 5. Acts as a pour point depressant. PA1 1. Lower maintenance costs by reducing the need to use costly pigging operations on pipelines, which requires at least a partial shut-down of the pipeline; PA1 2. Lower maintenance costs by reducing the problems associated with corrosion in pipelines; with both items "1" and "2" reducing the number of downtime stoppages in the pipeline; and PA1 3. Increase the throughput and flow rate of crude oil through pipelines. PA1 1. Recovery of at least 640,000,000 barrels per year of hydrocarbons (based on a daily production of 50,000,000 barrels), which results in a yearly recovery value of approximately $6.4 billion at a world crude oil price of $10.00/barrel. At a world crude oil price of $20.00/barrel the yearly recovery value would be $12.8 billion; PA1 2. The projected cost for use of the composition of matter described herein as a wax and asphaltene dispersant, liquefying agent, and demulsifier would range in price at 1999 costs from a low of about $0.05/barrel to a high of about $0.42/barrel, depending on the injection rate; and PA1 3. The overall maintenance costs associated with pipeline transport, marine tanker transport, and storage tank cleaning could be as much as $0.10/barrel of crude oil produced or $2.0 billion per year. PA1 The Chemistry and Technology of Waxes by Albin H. Warth, published by Reinhold Publishing Corp. (New York, 1947), p. 239 et al; PA1 Petroleum Refinery Engineering by W. L. Nelson, published by McGraw-Hill Book Co. (New York, 4.sup.th Ed., 1958), particularly Chapter 12 "DeWaxing"(pp. 374-75 et seq.); PA1 Physical Chemistry by Walter J. Moore, published by Prentice-Hall, Inc. (New York, 1955), particularly Chapter 16 "Surface Chemistry"(p. 498 et seq.); and PA1 chemical and process technology encyclopedia edited by Douglas M. Considine, published by McGraw-Hill Co. (New York, 1974), particularly its sub-section on "Waxes"(p. 1167 et seq.).
Since it acts as a wax liquefier and converts the wax to a less crystalline and more amorphous form, the slop oil waxes are readily dispersible into the crude oil medium. Thus a colloid is formed consisting of heavy paraffin wax and asphaltene compounds dispersed in crude oil. Since the preferred, exemplary composition of matter described herein also acts as a demulsifier, all water present in the slop oil mixture separates out, as well as the sand or grit present. The heavy paraffin wax and asphaltenes are dispersed as hydrocarbon into the crude oil and can be, for example, transported to the refinery for processing or to a marine tanker or other transport for shipment, for example, at ambient temperature.
The use of the preferred, exemplary composition of matter described herein, when, for example, injected into crude oil pipelines at, for example, the production source, is capable of keeping the heavy wax and asphaltenes dispersed in the crude oil. Having the wax and asphaltenes dispersed 100% into the crude oil will accomplish at least the following:
The main goal and objective of a crude oil pipeline company is, for example, to deliver to their customers a fixed amount of crude on an agreed-to, set schedule; every day that schedule is not met because of technical problems, the company loses money.
If the preferred, exemplary composition of matter described herein is mixed with crude oil loaded on, for example, marine tankers, the problems associated with wax deposits will be at least greatly inhibited, if not prevented from occurring, namely, slop oil residues will be greatly reduced and indeed prevented from forming. In, for example, oceangoing marine tankers the problems are twofold. At the end of many journeys the tankers have to go into drydock for maintenance due to corrosion caused by slop oil settling out and coating the walls of the tanks.
The benefits of the preferred, exemplary chemical composition described herein can be realized in, for example, the following ways:
In addition to the exemplary application of use with crude oil, there are many other applications of the principles and teachings of the present invention, as detailed and exemplified below, all with great utilitarian benefits.
For general background, "prior art" information pertinent to the invention, reference is had to: